Genome Run: Andean Shrub Is First New Plant Species Described by Its DNA

A flowering shrub from the Andean cloud forests made taxonomic history last month. The plant—now dubbed Brunfelsia plowmaniana—had puzzled botanists for decades as they endeavored to determine whether or not it was truly an evolutionary newcomer. When its DNA revealed this to be true, researchers made the unprecedented move to include B. plowmaniana's genetic code in its description as a new species, in the journal PhytoKeys. That decision could open the door to future DNA definitions of new botanical species—and heal a rift in the field of botany.

B. plowmaniana's saga began 30 years ago, when botanist Michael Nee approached ethnobotanist Timothy Plowman at The Field Museum in Chicago with specimens from a flowering shrub collected in the Bolivian mountains. A member of the nightshade family, Brunfelsia are known for their occasionally toxic and hallucinogenic properties, as well as their bright, color-changing flowers.

The particular species Nee presented to Plowman was labeled Brunfelsia uniflora—however, Nee and Plowman questioned the identification. Plowman had studied B. uniflora in the Brazilian lowlands, and it seemed improbable that the same plant had dispersed hundreds of kilometers into the cloud forests. Yet neither botanist was certain: "Plowman didn't know this specimen as a living plant, and I didn't know the Brazilian plant as a living plant," says Nee, now a botanist at The New York Botanical Garden. Convinced of a difference but unable to pinpoint it, Plowman continued to study and revise his writings on the brunfelsia genus until his death in 1989, yet he never solved the riddle.

More than two decades later, molecular biologist Natalia Filipowicz at the Munich Botanical Garden's herbarium reexamined the mysterious shrub. Filipowicz studied specimens from 50 species of Brunfelsia to characterize the genetic variation across the genus. When she reached the presumed B. uniflora of the Andes, she hit upon a set of genes that confirmed Plowman and Nee's suspicions. "Simply put," Filipowicz says, "the new species had unique DNA substitutions in the region that we studied." The substitutions proved that this Brunfelsia species was unique. Filipowicz and botanist Susanne Renner, director of the Ludwig Maximilians University of Munich Herbarium and Munich Botanical Garden, turned to Nee for a new physical description of the plant, and the trio published their description of Brunfelsia plowmaniana, named in honor of Timothy Plowman.

Including Filipowicz's genomic analysis prominently might seem like a logical choice, yet, despite dozens of other species confirmed in a similar manner, their description was a first. In fact, in 1996, the International Botanical Congress (IBC), which determines the code for naming new species, had roundly rebuffed an effort to publish species identification based primarily on genetic analysis. The reaction discouraged many in the field from similar efforts for years.

Why has the acceptance of molecular evidence taken so long? The delay is due in part to a long existing cultural divide in botany: On one side are botanists who work in the field and herbarium (storehouses for dried plants). On the other are those in the laboratory who put plants under the microscope or examine their chemical makeup. Although crossover does exist, increasing specialization has disproportionately given the task of naming a new species to the former group. "Traditionally, the people who work in the herbarium and name the plants never set foot in the lab— and the people in the lab are typically not the ones who name plants because they don't know how to and the rules are so arcane," Renner says.

Furthering the divide has been dispute over whether molecular analysis belongs in taxonomy at all. For example, DNA bar coding—in which biologists use specific genetic markers to distinguish between species—has been criticized by many taxonomists as an unreliable replacement for traditional methods. The bias in botany, not without foundation, questions the reliability of plant DNA markers, which pose challenges not found in animal genome sequences. For one thing, finding dependable markers in plant genomes is especially complex. Efforts to pinpoint a plant bar code have yielded two markers with about 70 percent discrimination success between species. By contrast, a single marker used to bar code animals has 95 percent discrimination success. Yet as molecular analysis becomes more sophisticated and less expensive, its acceptance has grown. Already, basic genetic sequencing in the field has become possible through portable kits. And botanists who are embracing the change hope that DNA extraction will bring new life to herbaria, which are treasure troves of plant samples that could hold centuries-old botanical secrets, such as the heritage or identity of new species.

The opportunity for a change in taxonomy came with an alteration to one of botany's most notorious naming rules: Until January 1 of this year, the International Code of Botanical Nomenclature stipulated that any new species include a "diagnosis," or brief statement identifying how this species differs from any other—written in Latin. The IBC finally decided to drop the requirement, instated in the 1930s but harkening back to the 18th-century father of taxonomy, Carl Linnaeus.

In the case of B. plowmaniana, it was Renner who made the bold suggestion of including the molecular analysis where the traditional Latin diagnosis would had been. Thanks to Nee's detailed description, the paper still included all of the typical components—physical description, geographic distribution and place in the family tree—of a new species discovery, in English. With the collaboration of both traditional field botanists and a molecular biologist, the authors hope that the B. plowmaniana discovery is the first of many papers—and future species discoveries—that build on botany's dual strengths.

"This is the bringing together of two cultures," Renner says. "There has been so much discussion of bar coding and genetics, and initially so much skepticism. But now it is definitely the way of the future. Not to replace one or the other side of botany, but to use both."